With a multi-electrode catheter, phased radiofrequency (RF) delivers current between each electrode and a backplate as well as between adjacent electrodes. This study compared the tissue heating and lesion dimensions created by phased and standard RF. Ablation was performed on the in vivo thigh muscles in 5 pigs. Six lesions were created on each thigh muscle using phase angle 0° RF, 127° RF, 180° RF with and without a backplate, and standard RF in bipolar and sequential unipolar configurations. Two plunge needles, each with 6 thermocouples 1 mm apart, were inserted into the tissue with one needle beside an electrode and the other midway between electrodes for tissue temperature measurement. The 0° RF created lower tissue temperatures and smaller lesions between electrodes than those beside electrode. With 127° and 180° RF, tissue temperature and lesion dimensions between electrodes were similar to beside electrode, while the 12° RF created higher tissue temperature and deeper lesions than 180° RF (both with and without a backplate) at both sites. Standard RF bipolar ablation created similar tissue temperatures and lesion depths at both sites, but required greater power than the 127° RF. Standard RF sequential unipolar ablation created only a slight temperature increase and no lesions between electrodes 3 and 4. As judged by tissue temperature, lesion depth and uniformity, and RF power requirement, 127° RF may be a better energy configuration for linear ablation than the other RF modalities tested.